MWN Blog: Summer arrives - quickly and with ferocity

Recap of Northwest Flow Week

The past week or so has seen the Mid-South region in a pattern frequently referred to as "northwest flow," which means that the upper level wind flows from northwest to southeast across the area. There are two main features of northwest flow in our area, and they are related:

Storm systems moving out of the central plains threaten the area. They commonly form into mesoscale convective systems (MCS's) and can deliver quite a punch if you are in their path (think Hurricane Elvis and others).
It is a very unpredictable pattern, in which the development, path, and demise of the systems can be hard to know more than a day or so in advance.

The image above shows departure from normal precipitation for the past week. While the Memphis area was fairly close to average, areas in eastern OK and western AR saw the brunt of heavy rainfall, while areas to our east also were above normal. (WeatherBell)

Overall we seem to have come through unscathed, as most either side-swiped the metro or fell apart before getting here. We got some rainfall but not excessive amounts, though a few downpours occurred, and temperatures stayed relatively mild due to the accompanying cloud cover of nearby systems. That pattern has ended today and we are quickly transitioning to a new one - the mid-summer "death ridge."

Arrival of the Death Ridge

Given its name because the strength of upper level high pressure (referred to as a "ridge" of high pressure when it is at upper altitudes) kills off pretty much all rain chances, the "death ridge" as it is colloquially known results in persistent heat, low cloud coverage, and thus minimal precipitation probabilities. Today is transition day as that ridge expands into the area.

The European model for the next 10 days shows anomalously high pressure build east over the southeast U.S. and southern Plains this weekend, then persist through most of the forecast period. that "death ridge" will be responsible for excessive heat and mainly dry conditions. (WxBell)

While not overly hot - in fact, just near average - it will be much warmer than the average day in the past week and you'll notice it. (Remember that yesterday at noon we were barely up to 70 degrees with light rain falling.) Some cloud cover is expected, but partly sunny skies won't hinder the high temperature from reaching the upper 80s. Combined with southerly wind at the surface, dewpoints in the upper 60s will result in sticky air in addition to the building heat. However, get your outdoor chores done today... it'll still be the coolest day of the next week, or more.

Mid-Summer Heat

The summer solstice isn't until June 21, but Mother Nature has other plans. Summer begins tomorrow. As the ridge overhead builds, and high pressure at the surface gains a foothold in the southeast U.S., the heat and humidity will feel like the middle of summer for the upcoming week. Daily high temperatures will be in the mid 90s with morning lows no lower than the mid 70s as southerly wind transports humid Gulf air into the region. There could be a few days where highs and lows are in the upper range of the 90s and 70s, respectively. That will put heat index readings in the mid 100s each afternoon and Heat Advisories may be required. Rain chances will be virtually nil until the latter part of the week.

The NWS National Blend of Models forecast temperatures for the next 10 days shows the outcome of the death ridge parking over the region. (weathermodels.com)

The early onset (seasonally), and persistence, of the heat will likely result in some heat-related concerns, especially for those not yet acclimated to the heat that must be outdoors. Be sure you are taking plenty of precautions when out - drinking plenty of water before and during exposure and applying sunscreen regularly. And PLEASE be sure that no pets or people are left in vehicles for any length of time!

By week's end, we'll see a cool front approach, and maybe move through, the area. But with limited deep-level moisture to work with and continuation of the ridging aloft, rain chances will be limited. Perhaps additional cloud cover will keep us a few degrees cooler on a day or two at week's end, but that remains to be seen. The ridge will reorient a bit by then, but looks to persist through next weekend and into the following week as well. It appears summer's arrival won't be fleeting. Stay cool, and play it safe outdoors!

Erik Proseus

MWN Meteorologist

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